1. Field of the Invention
The present invention relates to accumulation tables and, more particularly, to dynamic accumulation tables.
2. Related Art
A production line, such as a packaging line, is a series of machines. If the production line is designed without accumulation, the entire system would stop each time any piece of equipment stops. For example, if a machine is stopped for maintenance, then a production line without accumulation would require a complete shutdown of the entire line. Further, one machine may operate at a different speed from another. Without a means to compensate for the difference in operating speeds, machines would have to be turned on and off to adjust for the difference in cycle times. Therefore, accumulation greatly increases system efficiency and profitability.
Accumulation in the packaging industry is defined as having a reserve of containers between consecutive machines or a reserve of space to accumulate containers to provide for the inevitable machine stops. Accumulation is generally achieved with conveyors or with accumulation tables. The population, or density, of containers upstream and downstream of any machine, combined with the speed of each machine determines the amount of accumulation required.
In general, dynamic accumulation is accomplished through conveyors located between machines. Usually, a specified number of conveyors having a preconfigured width and speed are used for a given population rate. This approach requires large amounts of floor space and care must be used to control line pressure as the containers accumulate on the conveyors. Line pressure as understood in the packaging industry means the pressure placed on each container on the conveyor resulting from a large number of containers being forced together in a small area. If the number of containers entering the conveyor increases without simultaneously increasing the number of containers exiting the conveyor, line pressure results as the containers are forced against one another. Excessive line pressure can lead to scuffing of container labels and even breakage of some containers.
Another accumulation device is the bi-flow table. A bi-flow table has conveyor chains that run in opposite directions to re-circulate the containers. This approach has its limitations due to the noise and label damage generated by container-to-container contact during the re-circulating process.
Lastly, a loop system utilizes conveyors arranged in a loop configuration to re-circulate the containers and provide accumulation. In this system the containers that are not required by the downstream machine are sent on the re-circulating loop and merge again with the flow of incoming containers. A particular drawback of the loop system is that it is not easily reconfigured. For example, if greater accumulation is required, the loop system cannot easily be expanded. Further, most loop systems utilize a single continuous looped conveyor chain. Because there is only a single conveyor chain, containers must enter and leave the loop system at the same speed. In other words, containers maintain a constant speed on the loop system. Because the containers maintain a constant speed, it is not possible to have containers exit the loop system faster than containers enter, or vice versa.
Most loop systems have a gate adjacent the discharge area. The gate is used to prevent discharge and force the containers into an accumulation area. A problem associated with typical gates is that usually one or more containers in transmit within the discharge area of the table when the gate begins to close. Therefore, most conventional systems will encounter some jams from time to time due to having a container stuck between a flow separator and the gate. The common solution to this problem is to move the gate rapidly and attempt to close the gate between two containers. However, this can cause containers to become unstable and fall, thus causing even more jams.
Accumulation tables offer a more efficient alternative in terms of floor space utilization. However, typical accumulation tables have the same constraints as the conveyor systems with regards to line pressure, the inability to handle tapered containers, and a requirement to single-file the containers separately from the accumulation device. Further, most accumulation tables utilize custom components which increases costs of production and maintenance.
Further, most accumulation tables and the majority of loop systems lack adequate space to clean underneath the product conveying chains. As such, chain conveyor wear strips are difficult, if not impossible, to adequately clean.
Additionally, most accumulation tables lack a mounting space for the gate. Typically, a complex structure is attached to the sides or bottom of the accumulation table for mounting the gate above the conveyor chains of the accumulation table. In other words, the gate must be hung above the conveyor chains. This type of mounting is inherently weak and expensive.
There remains a need in the art for an accumulation table that provides for low pressure dynamic accumulation. Further, there remains a need in the art for an accumulation table that is scalable and which may operate at different container entry and exit speeds. Additionally, there remains a need in the art for an accumulation table that provides clearance for cleaning the conveyor chains, track sections, and associated wear strips. Finally, there remains a continuing need in the art to reduce the costs associated with the production and maintenance of accumulation tables.